810821 has 6 divisors (see below), whose sum is σ = 891366. Its totient is φ = 737000.

The previous prime is 810809. The next prime is 810839. The reversal of 810821 is 128018.

It can be written as a sum of positive squares in only one way, i.e., 662596 + 148225 = 814^2 + 385^2 .

It is not a de Polignac number, because 810821 - 2⁶ = 810757 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 810793 and 810802.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (810871) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 3230 + ... + 3471.

It is an arithmetic number, because the mean of its divisors is an integer number (148561).

2⁸¹⁰⁸²¹ is an apocalyptic number.

It is an amenable number.

810821 is a deficient number, since it is larger than the sum of its proper divisors (80545).

810821 is a wasteful number, since it uses less digits than its factorization.

810821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6723 (or 6712 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 20.

The square root of 810821 is about 900.4559955933. The cubic root of 810821 is about 93.2484588388.

Adding to 810821 its reverse (128018), we get a palindrome (938839).

It can be divided in two parts, 8 and 10821, that multiplied together give a palindrome (86568).

The spelling of 810821 in words is "eight hundred ten thousand, eight hundred twenty-one".